Aviation fuel cold flow additives and compositions

ABSTRACT

Aviation fuel, such as jet fuel, blends and methods for improving cold flow properties of such fuels at extremely low temperatures are disclosed. Cold flow properties of, for example, JP-8 based jet fuels are improved by addition to the fuel of a variety of C 10 -C 16  alkyl poly(meth)acrylate esters and polyvinylesters of C 10 -C 16  alkanoic acids. Demonstratable cold flow improvement of such fuels at temperatures of about −53° C. and below is shown.

CROSS REFERENCE TO RELATED APPLICATION

This application is a continuation of U.S. patent application Ser. No. 10/459,775 filed Jun. 12, 2003 and claims the benefit of the filing date of the aforesaid application under 35 USC §120.

FIELD OF THE INVENTION

The invention pertains to jet fuel blends and methods in which a cold flow enhancement agent is added to the jet fuel to improve fuel flow rates and flow characteristics at low fuel temperatures.

BACKGROUND OF THE INVENTION

It is important that aviation fuel exhibit a freeze point that is sufficiently low to allow adequate fuel flow through fuel system lines and filters to the engine. It is known that fuel temperature decreases as flight time increases and that longer duration flights typically require lower freezing point fuels than do shorter duration flights.

Additionally, high altitude flights, such as those conducted under some military operational conditions, also require lower freezing point fuels than do lower altitude conventional flights. Quite obviously then, there is a need to provide freeze point depressant/cold flow enhancement aids for aviation fuels, particularly for jet fuels, which will allow for sufficient fuel flow to desired combustion locations at the extremely low fuel temperatures encountered at high altitude and long duration flights. Publications WO 01/32811 A1 and WO 01/62874 A2 discuss details of aviation fuels and the need for lowered freeze point fuel blends.

One such means of enhancing the cold flow properties of wax containing hydrocarbon fluids is via chemical treatment. For example, use of poly[(meth)acrylates] as a pour point depressant for hydrocarbon lubricating oil is taught by U.S. Pat. Nos. 5,312,884 and 5,368,761.

WO 01/62874 A2 teaches the use of various chemical additives, including certain copolymers of vinyl acetate and ethylene, to lower the freeze point of aviation fuels. It is further taught that certain classes of pour point additives known to those skilled in the art for treating middle distillates, such as heating oils and diesel fuels, are not necessarily effective in the treatment of aviation fuel and actually may be detrimental.

U.S. Pat. No. 6,265,360 B1 teaches the use of transesterified acrylate polymer to improve the cold flow properties of wax-containing liquid hydrocarbons. It is speculated in the teaching that the additive can be prepared from a methacrylate and is effective in treating jet fuel. However, the untreated pour point of the responsive fluids was limited to −40° F. in the teaching and ranged from 75° F.-95° F. in the examples.

SUMMARY OF THE INVENTION

Methods for improving the cold flow rate of aviation fuels, and jet fuels in particular, are provided wherein the jet fuel is blended with a cold flow rate enhancement agent (CFREA). The CFREA is a polymer having a majority of repeat units as follows:

wherein R₁ is hydrogen, CH₃, or mixtures thereof; R₂ is —C(O)—O—, —O—(O)C—, —C(O)—NH—, or mixtures thereof; and R₃ is chosen from straight and branched C₁₀-C₁₆ alkyl groups. Preferably, the CFREA is a poly[C₁₀-C₁₆ alkyl methacrylate] or a poly[vinylester] of a C₁₀-C₁₆ alkanoic acid.

The invention will be further described in conjunction with the attached drawings and following detailed description.

BRIEF DESCRIPTION OF THE DRAWING

FIGS. 1 and 2 are graphs showing viscosity of certain test jet fuel/CFREA blends compared to a control sample.

DETAILED DESCRIPTION

In accordance with the present invention, it has been discovered that polymers having the repeat unit (a) as defined below are effective in depressing (lowering) the pour point of aviation fuel. Repeat unit (a) has the structure:

wherein R₁ is hydrogen, CH₃, or mixtures thereof; R₂ is —C(O)—O—, —O—(O)C—, —C(O)—NH—, or mixtures thereof; and R₃ is C₁₀-C₁₆ alkyl, or mixtures thereof and the like. Preferably, R₁ is CH₃; R₂ is —C(O)—O—; and R₃ is C₁₀₋₁₂ alkyl, mixtures thereof, and the like. Most preferably, R₁ is CH₃, R₂ is —C(O)—O—, and R₃ is C₁₂ alkyl.

As used herein, C₁₀-C₁₆ alkyl means any predominantly straight chain alkyl group having 10 to 16 carbon atoms per group. Most preferably, the alkyl groups consist of at least 90-mole % straight chain alkyl groups having 10 to 16 carbon atoms per group.

Exemplary monomers encompassed by the repeat unit (a) include, but are not limited to, alkyl methacrylates such as dodecyl methacrylate, lauryl methacrylate, tridecyl methacrylate, tertradecyl methacrylate, and hexadecyl methacrylate; alkyl acrylates such as dodecyl acrylate, lauryl acrylate, tridecyl acrylate, tertradecyl acrylate, and hexadecyl acrylate; N-alkylacrylamide such as N-dodecylacrylamide, N-laurylacrylamide, N-hexadecylacrylamide; N,N-dialkyl-acrylamide such as N,N-didodecylacrylamide; N-alkylmethacrylamide such as N-dodecylmethacrylamide, N-laurylmethacrylamide, N-hexadecyl-methacrylamide; alkyl vinyl esters such as vinyl decanoate and vinyl dodecanoate; and mixtures of any of the foregoing and the like.

The polymers of the present invention may be prepared via methods known to those skilled in the art, for example, see Allcock and Lampe, Contemporary Polymer Chemistry, (Englewood Cliffs, N.J., PRENTICE-HALL, 1981, chapters 3-5), and U.S. Pat. Nos. 5,312,884 and 5,368,761. Preferably, the polymerization is conducted in a hydrocarbon solvent employing an oil-soluble free radical initiator. The solvent may be any inert hydrocarbon and is preferably hydrocarbon oil such as Aromatic 100 (Exxon), HAN (Heavy Aromatic Naphtha (Exxon), or toluene that is compatible with the aviation fuel in which the polymer additive is to be subsequently used. Preferred classes of oil-soluble free radical initiators include, but are not limited to, the peroxides such as lauroyl peroxide and benzoyl peroxide, and azo compounds such as AIBN (2,2′-azobisisobutyronitrile).

Any of the conventional chain transfer agents known to those skilled in the art may be used to control the molecular weight. These include, but are not limited to, lower alkyl alcohols such as isopropanol, amines, mercaptans such as n-dodecyl mercaptan and t-dodecyl mercaptan, phosphites such as diethyl phosphite, thiaocids, allyl alcohol, and the like.

Branching agents known to those skilled in the art may also be used. These branching agents in this case are those compounds having two or more free radical polymerizable groups that can be either dissolved or dispersed in hydrocarbon solvent such as Aromatic 100 (Exxon), HAN (Heavy Aromatic Naptha), (Exxon) or toluene that is compatible with the aviation fuel in which the polymer additive is to be subsequently used. Examples of such branching agents include, but are not limited to, methylenebisacrylamide, 1,4-butanediol dimethacrylate, diallylurea, trimethylol propane trimethacrylate, polyethyleneglycol diacrylate, and the like and may form an optional repeat unit (b). The level of branching agent (repeatable unit (b)) utilized is limited to that which yields oil-soluble or oil-dispersible polymers. More preferably the amount of these branching agents, when used, ranges from about 10 ppm to about 5 mole % of the total monomer charge.

It is also known to those skilled in the art that the backbone of the polymers compositions of the present invention comprising the repeat unit (a) can optionally be modified to add functionality to vary their thermal stability. For example, the free radical polymerization can be conducted in the presence of from about 10 ppm to about 20 mole % of 2-methylene-1,3-dioxepane to insert ester linkages into the backbone of the polymer matrix.

Thus, an optional repeat unit (c) may also be present in an amount from 0-20 mole %. These repeat units (c) result from free radical ring opening polymerization of a cyclic monomer having the formula:

wherein R₄ is —O—, —S—, —N(CH₃)—, —CH₂— or mixtures thereof; and x is an integer from about 1 to about 3. Cyclic monomers included within this formula are known to undergo thermally initiated radical ring opening polymerization. For example, ring opening of 2-methylene-1,3-dioxepane will result in the incorporation of ester functionality in the polymer backbone according to the following:

Accordingly, the polymer may comprise repeat units (a), (b), and (c) wherein (b) when present, is present in an amount of about 10 ppm-5 mole % and (c) when present, is present in an amount of 10 ppm to about 20 mole %, repeat unit (a) is present in a molar amount of 100% minus (molar amount of (b) and (c))=molar amount (a).

Alternatively, the polymers of the present invention can be produced by transesterification of a poly[alkyl(meth)acrylate] by methods known to those skilled in the art, for example, see U.S. Pat. No. 6,265,360 B1. The starting poly[alkyl (meth)acrylate] is typically a hydrocarbyl acrylate polymer containing from 1 to 10 carbon atoms. Preferably, the starting poly[alkyl(meth)acrylate] would be prepared from a (meth)acrylate monomer with relative low cost such as methyl acrylate or methyl methacrylate. The alkyl groups are selected primarily with respect to the boiling point of the corresponding alcohols that are removed from the reaction mixture in the course of the transesterification reaction.

Generally, as the number of carbon atoms increases, the removal of the alcohols creates greater difficulties. The alcohols used for transesterifying of the starting poly[alkyl(meth)acrylate] include monohydric alcohols represented by the formula ROH, wherein R is a hydrocarbyl group of about 10 to about 30 carbon atoms. Although both primary and secondary alcohols can be used of the transesterification reaction, primary alcohols are preferred. Most preferred are primary alcohols having a linear hydrocarbyl structure. The transesterification reaction may be carried out in the presence of known transesterification catalysts. These include acids, bases, and lipase enzymes. The acids include mineral acids, sulfonic acids, as well as mixtures of these. The bases include alkali metal oxides, hydroxides, or alkoxides. The lipase enzymes include, but are not limited to, porcine pancreas lipase (PPL) and Novozyme 435. The transesterification reaction can be conducted in the present of high boiling aromatic or paraffinic solvents.

As would be understood by one skilled in the art in view of the present disclosure, it is intended that the aforementioned polymerization methods do not in any way limit the synthesis of the polymer of the present invention. Furthermore, it is to be understood that polymers comprising two or more different members from the repeat unit (a) group are also within the purview of the present invention. Preferred CFREA polymers in accordance with the above are the poly[C₁₀-C₁₆ alkyl (meth)acrylates] and/or polyvinyl esters of C₁₀-C₁₆ alkanoic acids.

The polymers of the present inventions should be added to an aviation fuel, for which improved cold flow performance is desired, in an amount effective for the purpose. In the preferred embodiment of the invention, the aviation fuel is selected from Jet Fuel A, Jet Fuel A-1, Jet Fuel B, JP-4, JP-8, and JP-8+100. Most preferably the jet fuel is a JP-8 based fuel such as neat JP-8 or the formulated JP-8+100.

Jet Fuel A and Jet Fuel A-1 are kerosene-type fuels with Jet Fuel B being a “wide cut” fuel. Jet A is used for many domestic commercial flights in the U.S. Most preferably, the CFREAs of the invention are used to increase the cold flow characteristics of military jet fuels such as JP-5, JPTS, JP-7, JP-8, and JP-8+100. JP-5 is currently used by the U.S. Navy with JP-8 and JP-8+100 used by the Air Force. These fuel types are summarized in the following Table 1. TABLE 1 U.S. Military Jet Fuel Freeze Year Point Flash Fuel Introduced Type ° C. Max Point Comments JP-5 1952 kerosene −46 60 JPTS 1956 kerosene −53 43 High thermal stability JP-7 1960 kerosene −43 60 JP-8 1979 kerosene −47 38 U.S. Air Force JP-8 + 100 1998 kerosene −47 38 U.S. Air Force, contains additives for improved thermal stability JP = jet propulsion Source: Chevron “Aviation Fuels” Technical Review.

On a 100% actives basis, the CFREA is preferably added to the jet fuel in an amount of about 1-7,500 mg/L of the jet fuel. More preferably, the CFREA is added in an amount of between about 250-5,000 mg/L, most preferably about 4,000 mg/L, as actives. The jet fuel/CFREA blend is capable of improving the cold flow rate of jet fuel, specifically, JP-8 based jet fuel at fuel temperatures on the order of about −53° C. to about −56° C. Experimental results have indicated that the CFREAs when blended with JP-8 based jet fuel in accordance with the invention improve cold flow rates of the fuel so that they are, as measured in accordance with Table 2 and the test system described, on the order of about 0.68 (g/s) and greater at fuel temperatures of about −53° C. to about −56° C.

The polymers of the invention can be employed in combination with conventional fuel additives such as dispersants, antioxidants, and metal deactivators. Such additives are known to those skilled in the art, for example see U.S. Pat. Nos. 5,596,130 and 5,614,081.

The jet fuel cold flow enhancement agents are preferably used in combination with an adjuvant component comprising an oil-soluble polar nitrogen-containing compound. These are set forth in U.S. Pat. No. 4,211,534 (Feldman) incorporated by reference herein. Basically, as stated in the '534 specification, these compounds are oil-soluble amine salts and/or amides that are generally formed by reaction of at least one molar proportion of hydrocarbyl acid having 1-4 carboxyl groups or their anhydrides with a hydrocarbyl substituted primary, secondary, and/or tertiary amine.

In the case of polycarboxylic acids, or anhydrides, all of the acid groups may be converted to amine salts or amides, or part of the acid groups may be left unreacted.

The term “hydrocarbyl” as defined is U.S. Pat. No. 4,211,534 includes groups that may be branched or straight chain, saturated or unsaturated, aliphatic cycloaliphatic, aryl, alkaryl, substituted derivatives thereof and the like. Typically, these hydrocarbyl groups will consist of from about 4-24 carbon atoms, more preferably 10-20 carbon atoms. In general, the resultant compound should contain sufficient hydrocarbyl content so as to be soluble in the fuel matrix.

Exemplary hydrocarbyl substituted acids and anhydrides include, but are not limited to, hexanoic acid, lauric acid, palmitic acid, steric acid, behenic acid, benzoic acids, 1,2,4,5-benzenetetracarboxylic dianhydride, 1,2-cyclo-hexanedicarboxylic anhydride, ethylenediaminetetraacetic dianhydride, salicylic acid, succinic acid, succinic anhydride, alkenyl succinic anhydrides, polyisobutenyl succinic anhydrides (PIBSA), phthalic acids, phthalic anhydride, naphthenic acids, naphthenic anhydrides, and the like. Particularly preferred is phthalic anhydride.

The hydrocarbyl substituted amines may be primary, secondary, or tertiary; preferably primary or secondary.

Exemplary hydrocarbyl substituted primary amines include, but are not limited to, coco amine, tallow amine, hydrogenated fatty primary amine, 2-ethylhexylamine, n-dodecyl amine, C₁₂₋₁₄ or C₁₆₋₂₂ tertiary alkyl primary amines from Rohm and Haas Company marketed under the trade name Primene®, mixtures thereof and the like. Particularly preferred is the C₁₆₋₂₂ tertiary alkyl primary amine marketed by Rohm and Haas Company under the trade name Primene® JM-T.

Exemplary hydrocarbyl substituted secondary amines include, but are not limited to, dicocoalkylamine, didecylamine, dioctadecylamine, ditallowamine, dihydrogenated tallowalkylamine, mixtures thereof and the like. Particularly preferred is dihydrogenated tallowalkylamine which is commercially available from Akzo Nobel Corporation under the trade name Armeen® 2HT.

As would be understood by one skilled in the art in view of the present disclosure, it is intended that the aforementioned examples do not in any way limit the description of the nitrogen-containing compounds. Furthermore, it is to be understood that ester analogs derived from a hydrocarbyl alcohol, and hydrocarbyl sulfo acid analogs such as those derived from o-sulphobenzoic acid or its anhydride, as described in European Patent Application 0261959, are also within the purview of the present invention.

An especially preferred group of polar nitrogen-containing compounds is the mixed amine salt/amides derived from reaction of hydrocarbyl acid (having two or more carboxyl groups) or its anhydrides as set forth above with a hydrocarbyl secondary amine. The resulting intermediate amide acid is then neutralized with a primary amine.

Generally, the preferred group of polar nitrogen-containing compounds can be represented by the formula

wherein Z is a divalent organic radical, R₅ and R₆ and R₇ are independently chosen from C₁₀-C₄₀ hydrocarbyl groups. The hydrocarbyl groups include straight or branched chain, saturated or unsaturated aliphatic, cycloaliphatic, aryl or alkylaryl moieties. These hydrocarbyl groups may contain other groups or atoms such as hydroxy groups, carbonyl groups, ester groups, oxygen, sulfur, or chlorine groups. As stated above, the hydrocarbyl groups may be on the order of C₁₀-C₄₀ with the range of C₁₄-C₂₄ even more preferred. The R₅, R₆, and R₇ groupings can also represent mixtures of different hydrocarbyl groups. Preferably, R₇≠R₅ or R₆.

The resulting compound should contain sufficient hydrocarbon content to be oil-soluble.

The preferred oil-soluble, polar nitrogen-containing compound is prepared by initial reaction of a hydrocarbyl acid or its anhydride and a secondary amine, such as the Armeen® 2HT. Then, the resulting mixed amine salt/amide is neutralized with a primary amine such as the commercially available Primene® JM-T product. Approximately equimolar amounts of the reactants are used, resulting in a mixed, substituted amide/amine salt.

The most preferred polar nitrogen-containing compound is an oil-soluble mixed amide/amine salt formed via reaction of equimolar amounts of phthalic anhydride with the secondary amine, Armeen® 2HT. The product of this reaction is then further reacted with an equimolar amount of the primary amine, Primene® JM-T to form benzoic acid, 2-[(bis(hydrogenated tallow alkyl)amino) carbonyl]-C₁₆-C₂₂ tert-alkyl amine salt having the structural formula:

wherein R₅ and R₆ are mixtures of C₁₆ and C₁₈ hydrocarbon from the commercially available tallowamine product, and R₆ is a mixture of C₁₈₋₂₂ hydrocarbons from the commercially available Primene® JM-T product.

The adjuvant nitrogen compounds can be used in amounts similar to those given above in conjunction with CFREA dosage.

The invention will be described further in conjunction with the following examples that are included for illustrative purposes only and should not be construed to limit the invention.

EXAMPLE 1 Preparation of Poly[lauryl methacrylate]

To a 300 ml four-necked reaction flask equipped with a mechanical overhead stirrer, thermocouple, reflux condenser, nitrogen sparge tube, addition port with septum and a heating mantle was added lauryl methacrylate (15.0 g, 96% purity), n-dodecyl mercaptan (0.15 g, 1.3% on a molar basis) and toluene (30 ml). The resulting solution was then heated to 100° C. under nitrogen sparge with mixing. An initiator solution comprising AIBN (0.23 g) dissolved in toluene (10 ml) was then added to the reactor at a rate of 0.077 ml/min. Upon completion of the initiator solution addition, the reactor was maintained at 100° C. for an additional two hours before cooling down to room temperature. The resultant solution was then concentrated in vacuo to remove the toluene solvent to produce the polymer additive.

EXAMPLE 2 Preparation of Poly[decyl methacrylate]

To the reactor set-up as described in Example 1 was added decyl acrylate (10.0 g, 100% purity), n-dodecyl mercaptan (0.12 g, 1.3% on a molar basis) and toluene (50 ml). The resulting solution was then heated to 100° C. under nitrogen sparge with mixing. An initiator solution comprising AIBN (0.155 g) dissolved in toluene (8 ml) was then added to the reactor at rate of 0.039 ml/min. Upon completion of the initiator solution addition, the reactor was maintained at 100° C. for an additional two hours before cooling down to the room temperature. The resultant solution was then concentrated in vacuo to remove the toluene solvent to produce the polymer additive.

EXAMPLE 3 Preparation of Poly[tridecyl methacrylate]

To the reactor set-up as described in Example 1 was added tridecyl methacrylate (15.0 g), n-dodecyl mercaptan (0.16 g, 1.3% on a molar basis) and toluene (26 ml). The resulting solution was then heated to 100° C. under nitrogen sparge with mixing. An initiator solution comprising AIBN (0.3 g) dissolved in toluene (8.7 ml) was then added to the reactor at a rate of 0.3 ml/min. Upon completion of the initiator solution addition, the reactor was maintained at 100° C. for an additional two hours before cooling down to the room temperature. The resultant solution was then concentrated in vacuo to remove the toluene solvent to produce the polymer additive.

EXAMPLE 4 Preparation of Poly[vinyl decanoate]

To the reactor set up as described in Example 1 was added vinyl decanoate (10.0 g) and toluene (26 ml). The resulting solution was then heated to 60° C. under nitrogen sparge with mixing. An initiator solution comprising AIBN (1.0 g) of dissolved in toluene (50 ml) was then added in one shot. Upon completion of the initiator solution addition, the reactor was maintained at 60° C. for an additional four hours before cooling down to the room temperature. The resultant solution was then concentrated in vacuo to remove the toluene solvent to produce the polymer additive.

EXAMPLE 5 Preparation of Poly[lauryl methacrylate]

To the reactor set-up as described in Example 1 was added Aromatic 100 solvent (15.0 g). The resulting solution was then heated to 90° C. under a nitrogen sparge with mixing. A monomer solution comprised of lauryl methacrylate (15.0 grams, 96%), and n-dodecyl mercaptan (1.6 grams) and Aromatic 100 solvent (15.0 g) was then added to the reactor at rate of 0.59 ml/min while simultaneously charging an initiator solution comprised of lauroyl peroxide (3.6 g) dissolved in toluene (20 g) at rate of 0.21 ml/min. Upon completion of the initiator solution addition, the reactor was maintained at 90° C. for an additional two hours before cooling down to the room temperature.

EXAMPLE 6 Preparation of Poly[lauryl methacrylate] with a Branching Agent

As in Example 5, except the monomer solution also comprised 1,4-butanediol dimethacrylate (0.12 g).

EXAMPLE 7 Preparation of Poly[lauryl methacrylate] Inserting an Ester Linkage into the Polymer Backbone

To the reactor set-up as described in Example 1 was added lauryl methacrylate (14.4 g, 96% purity), 2-methylene-1,3-dioxepane (0.33 g), n-dodecyl mercaptan (0.18 g, 1.3% on a molar basis) and Aromatic 100 solvent (25 ml). The resulting solution was then heated to 90° C. under nitrogen sparge with mixing. An initiator solution comprising AIBN (0.31 g) dissolved in toluene (12.62 g) was then added to the reactor at a rate of 0.15 ml/min. Upon completion of the initiator solution addition, the reactor was maintained at 90° C. for an additional two hours before cooling down to room temperature.

EXAMPLE A (Not of the Invention) Preparation of Poly[methyl acrylate] Precursor

A 2-liter four-necked reaction flask equipped with a mechanical overhead stirrer, thermocouple, reflux condenser, nitrogen sparge tube, two additional funnels, and a heating mantle. The first addition funnel was charged with methyl acrylate (200 g) dissolved in toluene (100 ml). The second addition funnel was charged with benzoyl peroxide (4 g, 97% purity) dissolved in toluene (615 g). The reaction flask was then charged with 75 g of methyl acrylate monomer solution form the first addition funnel and 125 g of benzoyl peroxide solution from the second addition funnel. The reaction flask was then slowly heated to 70° C. After maintaining 70° C. for 30 minutes, simultaneous drop-wise addition of the remaining methyl acrylate and benzoyl peroxide solutions were conducted over a period of 140 and 155 minutes, respectively. During the feeds an exotherm took place, raising the temperature to 105° C. Upon completion of the additions, the reaction temperature set point was raised to 100° C. Thirty minutes later, a solution of benzoyl peroxide (0.5 g) dissolved in toluene (10 ml) was added to the reaction flask in one portion. After maintaining the reaction temperature at 100° C. for an additional hour, heating was removed. The resultant polymer solution was then concentrated in vacuo to remove the toluene solvent to produce the poly(methyl acrylate) precursor.

EXAMPLE 8 Preparation of Transesterified Poly[methyl acrylate]

To a four-necked reaction flask equipped with a mechanical overhead stirrer, thermocouple, reflux condenser, nitrogen sparge tube, Dean-Stark trap and a heating mantle was added of Example A (20 g), toluene (50 ml), ALFOL 1012HA alcohol (29.5 g, a mixture of C₁₀, C₁₂ and C₁₄ alcohols available from Sasol North America), and ISOFOL 14 T alcohol (4.35 g, a mixture of C₁₂, C₁₄, and C₁₆ alcohols available from Sasol North America). The reaction mixture was then heated to 90° C. with stirring. Thereafter, methanesulfonic acid (0.78 g, 70% in water) was added to the reaction mixture in one portion. Forty minutes afterward, the reaction temperature set was raised to 140° C. After maintaining the reaction temperature at 100° C. for an additional five hours, heating was removed. The resultant polymer solution was then concentrated in vacuo to remove the toluene solvent to produce the poly[alkyl acrylate] additive.

EXAMPLE 9 Preparation of Poly[lauryl methacrylate]

As in Example 1 except at a larger scale (basis: lauryl methacrylate, 218.2 g, 96% purity).

The physical characterizations of Examples 1-9 are summarized in Table 2 below. The molecular weights were determined by GPC analysis referenced to poly[styrene] standards. TABLE 2 Polymer Additive Characterization Monomer Conversion Example (mole %) Mn Mw Mw/Mn 1 94.5 6900 14700 2.14 2 89.4 3450 6590 1.91 3 87.7 1350 11600 8.58 4 85.1 6480 34200 5.28 5 96.6 2359 3033 1.29 6 97.8 2116 2991 1.41 7 97.1 7386 11127 1.51 A 97.8 1500 50400 33.51 8 100.0 14300 104000 7.23 9 94.5 9098 20053 2.20

Screening results of the polymeric additive of the present invention in the CAST apparatus are provided in Table 3 below. In general, the CAST apparatus consists of two 500 ml flasks, one at atmospheric pressure and one sealed, connected via a ¼-inch Teflon tube. A known amount of fuel is charged to the flask at atmospheric pressure, and the apparatus is cooled to the desired test temperature in an environmental chamber. Once cooled to the desired temperature, vacuum (2-inch Hg) is applied to the sealed flask. The effectiveness of an additive is determined by measuring the time it takes for the fuel to flow to the sealed flask and the amount of fuel remaining in the atmospheric flask after the fuel flow ceases.

As shown in Table 3, at approximately −53° C., the untreated fuel has solidified and exhibited 100% hold up and essentially no fuel flow. Additions of the additive of the present invention to the fuel dramatically improved the cold flow properties at approximately −53° C. to −56° C. as evidenced by a substantial decrease in hold up and increase in fuel flow. TABLE 3 CAST Testing Results in JP-8 Fuel Conc. Fuel Temp Hold up Flow Rate Example # (mg/L)* (° C.) (%) (g/s) NA −53.5 100 NA 1 16000 −53.0 7 1.23 2 16000 −53.2 9 0.95 3 16000 −53.3 6 1.15 4 16000 −53.0 13 1.03 4 16000 −53.0 18 0.99 5 16000 −55.3 7 1.59 6 16000 −56.3 11 1.18 7 16000 −57.2 32 0.83 8 16000 −52.7 6 1.34 8 16000 −53.0 7 0.88 8 16000 −53.6 7 0.77 8 16000 −52.9 8 0.68 9 16000 −52.9 7 1.26 *25% active solutions

Description of the U-2 Wing Simulator Device is provided by Ervin, J. S. et al., “Investigation of the Use of JP-8+100 with Cold Flow Enhancer Additives as a Low-Coast Replacement for JPTS”, Energy & Fuels, 13, 1246-1251 (1999). Screening results for the polymeric additive of the present invention in the U-2 Wing Simulator Device are summarized in Table 4 below. As shown, at approximately −53° C., the untreated fuel exhibited significant hold-up. Addition of the additive of the present invention to the fuel dramatically improved the cold flow properties at approximately −53° C. as evidenced by a substantial decrease in hold up. TABLE 4 U-2 Wing Simulator Testing Results in JP-8 Fuel Tank Initial Final Hold Conc. Temp Weight Weight up Example (mg/L)* (° C.) (lbs) (lbs) (%) NA −49 196.5 192.0 2 NA −52 198.0 107.2 46 9 16000 −54 201.8 185 8 *25 wt % active solutions

When the polymeric CFREAs of the invention are conjointly used with an oil-soluble, polar nitrogen-containing compound adjuvant, both components can be provided in a convenient one drum approach, dissolved in a suitable organic solvent such as toluent, kerosene, HAN or the like. The polymeric CFREA is present in such compositions in a molar amount of about 0.01-100 moles polymeric CFREA to about 1.0 moles of the polar nitrogen-containing compound adjuvant. At present, it is preferred to use the polymeric CFREA, poly[lauryl methacrylate] and polar nitrogen-containing compound detailed in Example 12.

Additional CFREA polymers and an oil-soluble polar, nitrogen-containing compound used as an adjuvant treatment were prepared and tested as follows:

EXAMPLE 10 Preparation of Poly[lauryl methacrylate]

To a two-liter four-necked reaction flask equipped with a mechanical overhead stirrer, thermocouple, reflux condenser, nitrogen sparge tube, addition port with septum and a heating mantle was added lauryl methacrylate (96%, 218.2 g, 0.823 mole), n-dodecyl mercaptan (98.5%, 2.2 g, 0.01 mole) and toluene (400 ml). The resulting solution was heated to 95° C. under nitrogen sparge with mixing. An initiator solution consisting of 5.5 grams of 2,2′-azobisisobutyronitrile (AIBN) dissolved in 50 ml of toluene was then added to the reactor at a rate of 2.0 ml/min. Upon completion of the initiator solution addition, the reaction was maintained at 95° C. for an additional two hours before cooling to room temperature. The resultant solution was concentrated in vacuo to remove the toluene solvent, then diluted in Aromatic (Exxon) 100 to yield a 25 wt % polymer solution (i.e., 25% actives). 95.0% conversion of the monomer was determined by ¹H NMR.

EXAMPLE 11 Preparation of Poly[tridecyl methacrylate]

To a 300-ml four-necked reaction flask equipped with a mechanical overhead stirrer, thermocouple, reflux condenser, nitrogen sparge tube, addition port with septum and a heating mantle was added tridecyl methacrylate (100%, 60.0 g, 0.223 mole), n-dodecyl mercaptan (98.5%, 0.6 g, 0.003 mole) and Aromatic 100 (120 ml). The resulting solution was then heated to 90° C. under nitrogen sparge with mixing. An initiator solution consisting of 1.12 grams of AIBN dissolved in 40 ml of toluene was then added to the reactor at a rate of 1.1 ml/min. Upon completion of the initiator solution addition, the reaction was maintained at 90° C. for an additional two hours before cooling to room temperature. The resultant solution was then diluted further with A-100 to yield a 25 wt % active solution. 93.2% Conversion of the monomer was determined by ¹H NMR.

EXAMPLE 12 Preparation of the Nitrogen-Containing Adjuvant Compound Benzoic acid, 2-[(bis-(hydrogenated tallow alkyl)amino)carbonyl)]-C₁₆₋₂₂-tert alkyl amine salt

To a four-necked reaction flask equipped with a mechanical overhead stirrer, thermocouple, reflux condenser, nitrogen sparge tube, addition port with septum and a heating mantle was added phthalic anhydride (99%, 5.0 g, 0.03342 mole) and Armeen® 2HT (17.0 g, 0.03342 mole amine). The resulting wax mixture was then heated to 90° C. under nitrogen with mixing and held for four hours. Primene® JM-T (10.9 g, 0.03342 mole amine) was then added to the reactor at 90° C. over an eight-minute period, after which the batch was maintained at 90° C. for an additional four hours before cooling to room temperature to yield a wax like material. This was then diluted in Aromatic 100 to yield a 25 wt % solution of the nitrogen-containing compound.

EXAMPLE 13 Preparation of Benzoic acid, 2-[(bis-(hydrogenated tallow alkyl)amino)carbonyl)]-C₁₆₋₂₂-tert alkyl amine salt

This preparation was a scaleup of Example 12. To a four-necked reaction flask equipped with a mechanical overhead stirrer, thermocouple, reflux condenser, nitrogen sparge tube, addition port with septum and a heating mantle was added phthalic anhydride (99%, 344.74 g, 2.30 mole) and Armeen® 2HT (1165.75 g, 2.30 mole amine). The resulting wax mixture was then heated to 90° C. under nitrogen with mixing and held for one hour. Primene® JM-T (757.51 g, 2.3 mole amine) was then added to the reactor at 90° C. over an fifteen-minute period, after which the batch was maintained at 90° C. for an additional one hour before adding the Aromatic 100 solvent (6780.36 g) to yield a 25 wt % solution of the nitrogen-containing compound.

Screening results of the Examples 10-13 additives of the present invention in the CAST apparatus are provided in Table 5 below. As can be seen, at approximately −53° C. the untreated fuel has solidified and exhibited 100% holdup and essentially no fuel flow. Addition of the additives of the present invention as single component treatments to the fuel dramatically improved the cold flow properties at approximately −53° C. as evidenced by a substantial decrease in hold up and increase in fuel flow. In addition, blends of the polymeric CFREA with the polar nitrogen-containing adjuvant compound also exhibited improvement in the cold flow properties of the fuel. TABLE 5 CAST Testing Results in JP-8 Fuel Fuel Flow Additive Conc. Temp Holdup Rate Additive 1 Additive 2 Ratio (mg/L)* (° C.) (%) (g/s) None None N/A N/A −53.5 100 N/A Example 10 None N/A 8000 −52.7 7 1.38 Example 10 None N/A 16000 −52.9 7 1.26 Example 11 None N/A 8000 −53.6 7 1.35 Example 11 None N/A 16000 −53.3 6 1.15 Example 12 None N/A 8000 −52.7 10 1.34 Example 12 None N/A 16000 −53.3 9 0.93 Example 13 None N/A 12000 −57.8 25 0.47 Example 13 None N/A 12000 −55.1 7 0.85 Example 13 None N/A 14000 −57.0 13 0.83 Example 13 None N/A 14000 −55.2 10 1.06 Example 13 None N/A 16000 −57.1 8 0.82 Example 13 None N/A 16000 −55.2 8 0.93 Example 10 Example 12 50/50 6000 −53.3 13 1.34 Example 10 Example 12 50/50 16000 −54.8 15 1.50 Example 11 Example 12 50/50 6000 −53.1 7 1.50 *as 25 wt % active solutions, total addition

Low temperature viscosity studies of the treated fuel were carried out using a scanning Brookfield Viscometer in the temperature range of −5° C. to −60° C. as described by S. Zabarnick and M. Vangsness, Petroleum Chemistry Preprints 2002, 47(3), pp. 243-246 (2002). The results of this testing are given in Table 6. As used in the table, the “knee temperature” is defined as the temperature at which a rapid viscosity increase occurs due to crystal formation. It is desirable to have the knee temperature for a treated fuel to be shifted to a lower temperature relative to the neat fuel. It is also highly desirable to minimize the rate of viscosity increase as the fuel is cooled below the knee temperature.

It can be seen from the data presented in Table 6 that the additives of the present invention, as either stand alone treatments or as blends of the polymeric CFREA with the nitrogen-containing adjuvant compound, lower the knee temperature of the fuel. As shown in FIG. 1, blending the additives results in a significant reduction in the rate of increase of the viscosity of the fuel compared to use of one of the polymeric CFREA singly (compare curve “B” to curves “C”, “D”, and “E”).

FIG. 2 shows that, when the polymeric CFREA is utilized as a stand alone treatment, the rate of increase of the fuel are also effected by varying the molecular weight or use of a branching agent (compare curves “G” and “H” of FIG. 2 to “B” of FIG. 1). In addition, insertion of ester functionality into the backbone the polymeric CFREA did not adversely affect its cold flow enhancement properties (compare curves “H” of FIG. 2 to “B” of FIG. 1).

The following reference used in FIGS. 1 and 2 show viscosity versus temperature plot data for the following treatments in JP-8 fuel. Letter Additive 1* Additive 2* A None None B 16,000 mg/L Ex. 10 None C 12,000 mg/L Ex. 10  4,000 mg/L Ex. 12 D  8,000 mg/L Ex. 10  8,000 mg/L Ex. 12 E  4,000 mg/L Ex. 10 12,000 mg/L Ex. 12 F 16,000 mg/L Ex. 5 None G 16,000 mg/L Ex. 6 None H 16,000 mg/L Ex. 7 None *All dosages are in terms of 25 wt % actives.

TABLE 6 Low Temperature Viscosity Results - Knee Temperature in JP-8 Fuel Additive Conc. Knee Additive 1 Additive 2 Ratio (mg/L)* Temp (° C.) None None N/A N/A −52.0 Example 10 None N/A 16000 −55.7 Example 12 None N/A 16000 −54.0 Example 10 Example 12 50/50 16000 −56.4 Example 11 Example 12 50/50 16000 −56.0 Example 5 None N/A 16000 −55.1 Example 6 None N/A 16000 −54.9 Example 7 None N/A 16000 −55.5 *25 wt % actives

While the specification above has been drafted to include the best mode of practicing the invention as required by the patent statutes, the invention is not to be limited to that best mode or to other specific embodiments set forth in the specification. The breadth of the invention is to be measured only by the literal and equivalents constructions applied to the appended claims. 

1. Method of improving the cold flow rate of jet fuel comprising adding to said jet fuel an effective amount for the purpose of a polymeric cold flow rate enhancement agent (CFREA) having (a) repeat units characterized by the formula

wherein R₁ is hydrogen, CH₃, or mixtures thereof; R₂ is —C(O)—O—, —O—(O)C—, —C(O)—NH—, or mixtures thereof; R₃ is C₁₀-C₁₆ alkyl, or mixtures thereof, repeat units (b) from 0 to 5 mole percent of a branching agent, and (c) from 0 to 20 mole percent of a repeat unit resulting from free radical ring-opening polymerization of a cyclic monomer characterized by the formula

wherein R₄ is —O—, —S—, —N(CH₃)—, —CH₂— or mixtures thereof; and x is an integer from 1 to
 3. 2. Method as recited in claim 1 comprising adding from a 1-7,500 mg of said CFREA to said jet fuel, based upon 1 liter of said jet fuel.
 3. Method as recited in claim 1 wherein said jet fuel is a JP-8 based jet fuel.
 4. Method as recited in claim 1 wherein said CFREA is a C₁₀-C₁₆ alkyl poly(meth)acrylate ester.
 5. Method as recited in claim 1 wherein said CFREA comprises a mixture of C₁₀-C₁₆ alkyl poly(meth)acrylate esters.
 6. Method as recited in claim 1 wherein said CFREA is a polyvinylester of a C₁₀-C₁₆ carboxylic acid.
 7. Method as recited in claim 5 wherein said CFREA is poly(vinyldecanoate).
 8. Method as recited in claim 4 wherein said CFREA is polylauryl(meth)acrylate.
 9. Method as recited in claim 4 wherein said CFREA is polydecylacrylate.
 10. Method as recited in claim 4 wherein said CFREA is polytridecyl(meth)acrylate.
 11. Method as recited in claim 1 further comprising adding, as an adjuvant treatment to said jet fuel about 1-7,500 mg/L of an oil-soluble, polar nitrogen compound to said jet fuel.
 12. Method as recited in claim 11 wherein said oil-soluble, polar nitrogen compound comprises an amine salt or amide.
 13. Method as recited in claim 12 wherein said oil-soluble polar nitrogen compound comprises a reaction product formed from reaction of a hydrocarbyl acid having two or more carboxyl groups, or anhydride thereof, and a hydrocarbyl secondary amine followed by neutralization of the resulting product with a hydrocarbyl primary amine.
 14. Method as recited in claim 11 wherein said oil-soluble, polar nitrogen compound is benzoic acid, 2-[(bis(hydrogenated tallow alkyl)amino)carbonyl]-C₁₆-C₂₂ tert-alkyl amine salt.
 15. Composition for improving the cold flow rate of jet fuel said composition comprising, in an organic solvent medium, 1) a polymeric cold flow rate enhancement agent (CFREA) having (a) repeat units characterized by the formula

wherein R₁ is hydrogen, CH₃, or mixtures thereof; R₂ is —C(O)—O—, —O—(O)C—, —C(O)—NH—, or mixtures thereof; R₃ is C₁₀-C₁₆ alkyl, or mixtures thereof, repeat units (b) from 0 to 5 mole percent of a branching agent, and repeat units (c) having from 0 to 20 mole percent of a repeat unit resulting from free radical ring-opening polymerzation of a cyclic monomer characterized by the formula

wherein R₄ is —O—, —S—, —N(CH₃)—, —CH₂— or mixtures thereof; and x is an integer from 1 to 3; and 2) an oil-soluble, polar, nitrogen-containing compound.
 16. Composition as recited in claim 15 wherein 1) is present in an amount of about 0.01-100 moles of 1) per one mole of 2).
 17. Composition as recited in claim 15 wherein said oil-soluble polar nitrogen-containing compound is an amine salt and/or amide.
 18. Composition as recited in claim 17 wherein said oil-soluble, polar nitrogen-containing compound is a reaction product formed by reaction of a C₄-C₂₄ hydrocarbyl acid or anhydride thereof with a C₄-C₂₄ hydrocarbyl substituted primary, secondary, and/or tertiary amine.
 19. Composition as recited in claim 18 wherein said oil-soluble, polar nitrogen containing compound comprises a reaction product formed from reaction of a hydrocarbyl acid having two or more carboxyl groups or an anhydride thereof and a hydrocarbyl secondary amine followed by neutralization of the resulting product with a hydrocarbyl primary amine.
 20. Compositions as recited in claim 15 wherein said oil-soluble, polar nitrogen compound is benzoic acid 2-[(bis(hydrogenated tallow alkyl)amino)carbonyl] C₁₆-C₂₂ tert-alkyl amine salt.
 21. Composition as recited in claim 19 wherein said CFREA is polylauryl(meth)acrylate.
 22. Composition as recited in claim 20 wherein said CFREA is polylauryl(meth)acrylate. 